1. Field of the Invention
This invention relates to gear and transmission lubricant compositions, having improved sludge-dispersibility, particularly, those useful for automotive gear and transmission fluids.
2. Description of the Prior Art
Heretofore, in order to improve anti-wear or lubricating qualities and sludge-dispersibility, required for automotive gear and transmission fluids, there have been known those containing added thereto anti-wear or lubricating agents comprising phosphorus-containing organic compound, such as phosphate or phosphite esters or amine salts thereof, together with lower molecular weight dispersants, such as succinimides and benzyl amine. For example, U.S. Pat. No. 4,800,029 discloses an automatic transmission fluid (ATF) comprising a solvent-purified 150 neutral oil, containing added thereto an oleamide phosphate as anti-wear agent and polybutenyl succinimide as dispersant.
These fluids containing added thereto phosphorus-containing organic compounds together with lower molecular weight dispersants, however, have drawbacks, such that dispersabilities become insufficient under severe service conditions likely to form larger sludge, encounterd with friction or wear, accompanied with recent tendency of miniturization and output power up of automobiles; and it is desired to improve the dispersibility.